1. Field of the Invention
The present invention relates to an inkjet printing apparatus, an inkjet printing method, a program, and a storage medium that perform reciprocal printing.
2. Description of the Related Art
The use of information processing apparatuses, including but not limited to copying apparatuses, fax machines, word processors, or computers, to say nothing of all types of communications devices, is spreading rapidly. One class of these devices is a printing apparatus that uses an inkjet protocol printhead to perform digital image printing.
In order to increase the printing speed, a printhead, which integrates a plurality of orifices that discharge ink, also known as nozzles, and fluid channels, is used with such inkjet protocol printing apparatuses, in the form of a printing element array that organizes a plurality of printing elements. When providing support for colorization, a printhead is used that comprises a plurality of printing element arrays that support each color.
Unlike a printhead of a black-and-white printer that only prints text, printing a full-color image demands that a range of conditions be satisfied, including but not limited to color development, tonality, and uniformity. In order to print high-quality full-color images, therefore, it is necessary to control the printhead in a manner that takes a variety of factors into account.
Of particular concern with regard to uniformity are the slight discrepancies that arise in the course of the process of manufacturing the printhead printing element array. That is, the various volumes and facings of direction of the ink discharged from the various nozzles vary subtly when using a printhead with dispersion at the nozzle level to perform the printing of a full-color image. Consequently, unevenness emerges in density in the ultimately printed full-color image, which is a cause of degraded quality in the printed image. A multi-pass printing method has accordingly been proposed that is capable of minimizing the unevenness of density, by having a given printhead use print scanning to gradually print equal printing areas, using different nozzles to perform a plurality of printhead printing scans.
So-called multi-pass printing involves using different nozzles per printing scan to print all print pixels within the image area in a single printing scan, which halves the impact that unevenness of density, caused by specific nozzle discrepancies would have on the printed image, which noticeably alleviates unevenness of density in full-color images as printed on printing paper.
When performing multi-pass and reciprocal scanning, however, priority color varies depending on ink stamping sequence, in the forward scanning direction and the reverse scanning direction, resulting in a rendering of differing colors vis-à-vis human visual capabilities.
For example, consider a four-color head, which uses a printhead with printing colors positioned, from right to left, Black (Bk), Cyan (C), Magenta (M), and Yellow (Y), and performs print scanning by moving the printhead reciprocally in the direction of the four-color head array, i.e., the left-right direction. Forward scanning by the printhead discharges ink from the respective nozzle arrays and prints the image in the left-hand direction, and reverse scanning by the printhead discharges ink from the respective nozzle arrays and prints the image in the right-hand direction.
In these circumstances, the printing sequence for each color on printing paper follows the four-color printhead array sequence; for example, if a green signal, i.e., cyan+yellow, is input into a given area, then ink is absorbed into all pixels in the order of cyan, followed by yellow. Therefore, cyan is the priority color, as it is absorbed first in the scanning sequence when the printhead moves to the left, and a cyan-enhanced green dot will be formed on the printing paper.
Conversely, reverse scanning, which moves the printhead to the right, also reverses the ink absorption sequence. Put another way, reverse scanning results in ink being absorbed yellow first, followed by cyan, forming a yellow-enhanced green dot on the printing paper. Having the printhead repeat such reciprocal scanning results in forming a region comprising cyan-enhanced green dots and yellow-enhanced green dots, depending on printing by forward scanning, or by reverse scanning.
If printing paper advance is performed at the width of the printhead for the respective scans, the area of cyan-enhanced green and the area of yellow-enhanced green are mutually repeated, corresponding to the width of the printhead. Consequently, color discrepancies arise per print scan in printed images that are supposed to have uniform greens, thus giving rise to significant image degradation.
Furthermore, greater high-speed printing and high-image quality printing are being demanded in current times, and the multi-pass printing method wherein a printhead partitions printing scans into a plurality of scans, is undesirable for printing apparatuses, as it doubles the printing time where printing is concerned, at a minimum.
U.S. Pat. No. 6,315,387 proposes an inkjet printing apparatus such that the sequence wherein the order in which ink is overlaid is the same for the forward scan and reverse scan, and that the printing element array, corresponding to the various printhead inks, is symmetric in the main scan direction.
By using printheads with such arrangements to perform reciprocal scanning, color discrepancies in printed images that would originate in the ink application sequence are minimized. Furthermore, it is also possible to achieve high-speed printing in multi-pass printing without increasing the number of printhead scans.
Japanese Patent Laid-Open No. 2001-171151 discloses an inkjet printing apparatus that positions a printhead printing element array of Bk, C, M, Y, M, and C, and interchanges the M and C printing elements used in printing in forward printing and reverse printing.